1. Field of the Invention
This invention relates to a system for controlling power to multiple a.c. lighting loads from both local controls and a central location.
2. Description of the Related Art
Systems are known for controlling lighting loads from both a master control and from local controls that are near the loads.
Remote control master switching systems are available from General Electric. These systems include master selector switches to provide individual local control or master control. A similar system is available from Touch-Plate International, Inc., of Emeryville, CA.
Centrally-controlled dimming systems are available from LiteTouch, Inc. and from Electro Controls Inc., both of Salt Lake City, UT.
The Touch-Plate, LiteTouch, and Electro Controls master control systems all use a remote power control panel that contains triacs and relays to control (i.e., to dim or switch) the power to the load. The controls for the system include a centrally located master station and, dispersed throughout a building, buttons to turn the lights on and off or to provide "raise/lower" dimming of the lights. Raise/lower dimming is accomplished by pushing a button to raise or lower the power to the lighting load. When the desired level is reached, the button is released.
Another system for central dimming of lighting is available from Lightolier Controls, Secaucus, NJ. That system involves multiple local ("Easyset") controls that can provide raise/lower dimming. Multiple Easyset dimmers can be operated through a single master; however, they must all be on the same circuit, which, in accordance with the National Electrical Code, limits total power to 2000 W.
A number of these systems include indicator lights to show system status at the local and/or master controls; however, each has a common drawback. The local controls can only dim, if at all, by the raise/lower method. This dimming method does not permit light levels to be changed rapidly, nor does the dimmer actuator position provide a visually-apparent indication of lighting level.
Lutron Electronics Co., Coopersburg, PA provides central dimming and switching control of multiple zones of lighting with Versaplex.RTM. and Aurora.RTM. dimming systems. These systems do not include wallbox dimmers dispersed to the spaces in which lighting is being controlled, instead requiring centralized power cabinets.
A system available from Enercon Data Corp., of Minneapolis, MN, uses power relays, which can be mounted in junction boxes, throughout a building and can be locally or centrally switched. In order to dim an area with this system, a standard dimmer may be located near the load; however, the enabling switch that turns power to the dimmer on and off must be separated from the dimmer by a physical barrier (for reasons discussed below). As a result, separate dimmers and switches are required, increasing the number of controls on the wall and complicating the wiring.